Abstract
Some effects of the sea anemone toxin, ATX-II, on vertebrate skeletal muscle have been described. At a concentration of 1 X 10(-7)-1 X 10(-6)M, ATX-II caused a sodium-dependent depolarization of the muscle fibres of the rat soleus and extensor digitorum longus, of the mouse soleus and extensor digitorum longus and of the chicken posterior latissimus dorsi. The muscle fibres of the frog sartorius were insensitive to the toxin. Action potentials generated by direct stimulation were prolonged by ATX-II, but the degree of prolongation was variable. Chicken posterior latissimus dorsi muscle fibres were most sensitive in this regard, and mouse extensor digitorum longus were least sensitive. Both denervated and immature muscle fibres were more sensitive to ATX-II than mature innervated muscle fibres. The sensitivity to ATX-II declined rapidly as muscle fibres matured. In some muscles, the prolongation of the action potential was enhanced by repetitive stimulation, but not by the passive depolarization or hyperpolarization of the muscle fibres. The actions of ATX-II could be reversed by washing in all but the innervated soleus of the mature rat.